Some of the most important decisions that older adults make are about medical care. These decisions can be very complicated, as they often involve a number of different options, each with its own burden of treatment and possible outcomes. Medical-treatment choices typically involve high levels of uncertainty regarding the possible outcomes of each available treatment. While we know a great deal about decision- making under uncertainty in young adults, research on age-related changes in choice behavior is scarce, and mostly focuses on simple financial decision-making. Financial decision-making is also the focus of most of the research which examined the neural mechanisms of decision-making processes, even in young adults. We know that regions in the prefrontal and parietal cortices, as well as basal ganglia circuits, take part in these processes, and we also know that these same brain areas experience structural thinning, reduction in dopaminergic receptors and changes in activation patterns in aging. We do not know, however, whether choice behavior in the monetary domain can predict choices in other types of significant personal decisions that older adults face, such as medical decisions. We also do not know whether age-related changes in uncertainty attitudes and their underlying neural patterns follow similar trajectories i the monetary and the medical domains. In this application we propose to combine economic, psychological and neurobiological approaches to the study of decision-making under uncertainty in the medical and monetary domains in young and older adults, in an effort to characterize these decision processes at the behavioral and neurobiological levels. Our approach is built on behavioral economics analysis, which suggests that decisions under uncertainty are affected not just by the individual's assessment of outcomes and their probabilities (risk attitude), but also by the individual's sensitivity to missing information about these probabilities (ambiguity attitude). Combining experimental economics techniques with functional and structural MRI we will be able to characterize individual attitudes towards risk and ambiguity in each decision domain, and to look for the neural correlates of these individual attitudes. In a group analysis we will compare these behavioral and neuronal characteristics between young and older adults. The proposed studies are likely to lead to significant insights into the behavioral and neurobiological processes that underlie decision-making in elders, and thus are likely to contribute to improving the quality of life of a large proportion of the population.